Electroluminescent display device

ABSTRACT

This disclosure provides an electroluminescent (&#34;EL&#34;) display device having anode, cathode, insulator and organic EL layers. The anode and cathode layers sandwich the other two layers, and the insulator layer is patterned to selectively block flow of current through the EL layers, and thereby locally block generation of light. The patterned insulator layer allows a single panel to display multiple visual attributes, yet does not require electrode patterning. The patterned insulator can be fabricated using photoresist exposure and development procedures. The photoresist is laid on top of a commercially available substrate/electrode layered pair, and is developed to create an assembly that can be completed in a single vacuum deposition process. By etching a small region of the electrode from the commercially available layered pair, and by choosing a deposition frame that blocks deposition on a second, different small region, electrical terminals may be coupled to the panel with a reduced risk of an electrical short.

The present invention relates to an electroluminescent display device.

BACKGROUND

Electroluminescent ("EL") display devices are becoming increasinglypopular, due in-part to cheaper fabrication and longer life provided byimprovements in thin-film technology. Typically, the EL devices areformed of a number of transparent layers, including an EL layer whichgenerates light when electricity flows through it. In addition to the ELlayer, the devices also generally include a substrate and two electrodes(a cathode and an anode) on top of the substrate, with the EL layersituated between the electrodes. The EL layer can be formed from eitherinorganic or organic EL materials, each having its own chemistries,fabrication procedures, advantages and disadvantages.

As with other electronic display devices, EL devices can be made to bestatic or addressable. In the former case, a "static" EL device has asingle display element which is turned "on" to display one image only;the image can be complex, meaning that it contains many visualattributes, but it is always turned "on" or "off" as a single unit,e.g., as a single pixel. In the latter case, an addressable EL devicecan include many rows and columns of single-pixel display elements, eachof which typically represents a single visual attribute, and can beselectively controlled and illuminated so that the pixels collectivelyreproduce any desired image. EL devices of the latter type havedrawbacks, however; often, it is difficult to fabricate or electricallyconnect the multiple rows and columns of display elements in a mannerthat they are close together and provide high resolution. Since manyindividual display elements usually make-up the display, brightness canvary widely between elements over time, since some pixels tend to beilluminated more frequently than others. Finally, it is expensive tofabricate these types of EL devices.

For these reasons, and due to relative simplicity of construction of asingle element which unchangingly represents a complex image, static ELdevices are sometimes best suited for use in many applications. As usedherein, term "pixel" will be used to refer to the smallest addressablepart of a display that can independently be switched "on" and "off."This disclosure relates to a static EL display element, that is, to asingle pixel EL device which represents a complex image, having manyvisual attributes.

FIGS. 1A and 1B illustrate one prior art static device that displays anarbitrary image consisting of the re-entrant alphanumeric character "®."In particular, FIG. 1A shows a cross-section of a display device 41which includes multiple thin-film layers, including a substrate 43, afirst electrode 45, an EL layer 47 and a second electrode 49. Thecharacter "®," seen in FIG. 1B, is formed by patterning one of theelectrodes 45 or 49, to have the shape of the character; in this manner,when the display is turned "on," electric current will flow through theEL layer 47 and generate light, but only in areas between the twoelectrodes 45 and 49, to illuminate the character "®."

In FIG. 1B, an electrode 51 is patterned during fabrication to representmultiple visual attributes of the desired image. Since the attributesare part of a single pixel display, each portion 53 of the image whichis to be illuminated must overlie the electrode 51 and have a continuouselectrical path to a terminal 57; for this reason, the electrode layer51 is typically patterned in a manner that it is continuous across allof the illuminated portions 53 of the image; the electrode 51 connectsthem (a) together via a bridge 55 and (b) to the terminal 57 via aconnecting path 59.

Again with reference to FIG. 1A, the particular one of the electrodeswhich is patterned (in the form of electrode 51) can be chosen to beeither the first electrode layer 45 or the second electrode layer 49; inFIG. 1A, it is indicated to be the second electrode layer 45. Which everelectrode layer is chosen, patterning results in a display whereundesired portions of the conductor, e.g., the bridge 55 and connectingpath 59 of FIG. 1B, are necessarily always illuminated along with thecharacter "®" when the display device is switched "on." That is to say,the connecting bridges and paths of an image typically can not beeliminated from the display.

Selecting the first electrode layer 45 for patterning (the one closestto the substrate 43) typically requires a shadow mask or chemical etchprocedure, which must be designed to provide a continuous electrodepath, including the bridge 55 and connecting path 59. Since a patternedmetal layer formed by a chemical etch or shadow mask procedure may tendto have sharp corners (not shown in the context of a first, patternedelectrode layer, but designated 48 with respect to the second electrodelayer 49 of FIG. 1A), use of a patterned first electrode layer 45 posesheightened device reliability problems (due to possible electricalshorting between electrodes 45 and 49) and requires special attentionwith respect to thickness and uniformity of the EL layer 47.

On the other hand, if the second, top electrode layer 49 of FIG. 1A isto be patterned, then this is typically performed during, orintermittent to, a vacuum deposition process of the EL layer 47 and thesecond electrode layer 49, since a shadow mask must be maneuvered intothe deposition path. Practically speaking, insertion of a shadow mask istypically performed by interrupting a vacuum deposition process toinsert the mask over the device 41 following deposition of the EL layer47. Since individual thin film layers of the display device may alsoreact adversely with air (forming undesired oxides), patterning of asecond electrode layer generally also adds to complication, delay andexpense of fabrication of the EL device, and detracts from its usefullife. Also, as indicated in FIG. 1A, a patterned second electrode layer49 typically leaves the EL layer exposed to air, and the secondelectrode layer 49 susceptible to water denigration by lateral seepage.The design factors just described also detract from large scale paralleldevice fabrication (using mass chip fabrication technologies, forexample). For these reasons, conventional electrode patterningtechniques present some significant drawbacks.

A definite need exists for a single element EL device which may be usedto represent multiple attributes, yet which does not feature undesiredillumination of conductor paths. Still further, a need exists for an ELdevice which may be used to present a smooth display with a very highlevel of resolution. Ideally, for example, such an EL device could beused to display photographic images. A need also exists for a means ofcreating a display which does not require interruption of a vacuumduring the fabrication process, and hence, which is a simpler, morereliable process, and which features better economies of scale forsimultaneous, parallel device fabrication. Finally, a need exists for asimpler, less expensive fabrication procedure. The present inventionsolves these needs and provides further, related advantages.

SUMMARY

The present invention solves the aforementioned needs by providing an ELdevice and related method that does not require electrode patterning;rather, the device makes use of an insulator which is readily patternedto represent any desired image, including photographic or computerimages. The patterned insulator locally blocks the flow of currentwithin the device, to thereby block light generation, hence highlyintricate electrode patterning is not needed to create a specific image.The present invention enables creation of a display that does notrequire conductive bridges or paths which are illuminated along with thedesired image; it provides for a more accurate, detailed image at nearlyany level of resolution.

Moreover, since the present invention does not require electrodepatterning, it provides for device manufacture that (1) does not requirevacuum interruption and a large number of processing steps, and hence ismore easily and less expensively performed, and (2) is more amenable tosimultaneous, parallel device manufacture using conventional filmdeposition techniques. As can be seen, therefore, the present inventionprovides an EL device that produces better images and is easier tofabricate.

One form of the present invention provides an EL device having a cathodeand an anode that together sandwich EL material between them, and apatterned insulator, deposited between the EL material and one of thecathode and the anode. The insulator is employed to impart variedelectrical insulation between the cathode and the anode at differentregions of the display. Thus, the insulator helps form and distinguishconductive regions of the display, where current may flow through the ELmaterial, and thereby generate light, and impeded regions of thedisplay, which block current, and thereby retard light generation.Utilizing this construction, the EL device of the present inventionfacilitates use of a continuous, uninterrupted vacuum deposition processto deposit metal electrode layers of the device.

In more detailed aspects of this form of the invention, the EL device isconstructed to have at least three regions: one region having anodematerial, but no cathode material; one region having cathode material,but no anode material; and one region having cathode material and anodematerial and EL material. This construction permits terminal fabricationwithout danger of breaking through layers, and thereby unintentionallyshorting the display during device fabrication.

Also, in other more detailed features of the invention, the insulatorcan be formed with a simple photoresist material and a computer printouton transparency, for use as a photoresist mask. In this manner, and withthe cooperation of suitable image software, nearly any image, includingphotographic images, may be used to pattern the undeveloped photoresistinto the developed, patterned insulator.

A second form of the invention relates to a method of fabricating an ELdevice having various ones of the features just described. In thepreferred implementation of this second form of the invention, aprefabricated assembly, including a substrate, one electrode (the anodeor cathode) and a patterned insulator can be created in a first process,prior to a second process which includes vacuum deposition of theremaining EL device layers atop the prefabricated assembly. In formingthe prefabricated assembly, a portion of the first electrode ispreferably removed to fabricate a first region which, once completed,will have second electrode material (but no first electrode material).The patterned insulator is also added during this formation process, byany one of a number of procedures. Once the prefabricated assembly hasbeen created, it can be covered with a suitable frame (a mask used forthe vacuum deposition process, not to be confused with a photoresistmask preferably used to pattern the insulator), and the EL material,second electrode material and an anti-oxidation cap can be added in asingle vacuum process. The frame is selected to have a geometry thatblocks deposition of the second electrode material (and preferably, italso blocks deposition of the EL material and cap layers) in a small,second region of the display which is different from the first region.In this second region, the display will have exposed first electrodematerial, but no second electrode material. The second region is usedfor a second electrical terminal.

The invention may be better understood by referring to the followingdetailed description, which should be read in conjunction with theaccompanying drawings. The detailed description of a particularpreferred embodiment, set out below to enable one to build and use oneparticular implementation of the invention, is not intended to limit theenumerated claims, but to serve as a particular example thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-section of a prior art electroluminescent ("EL")display device.

FIG. 1B is an illustrative diagram of one layer of a device of FIG. 1Aand, in particular, indicates the appearance of a metal electrode usedto form the re-entrant alphanumeric character "®," as well as appearanceof the device when illuminated.

FIG. 2 is an illustrative cross-sectional diagram of an organic EL panelmade according to the principles of the present invention and, inparticular, is used to illustrate the different thin-film layers of thepanel.

FIG. 3 is a top illustrative view of a finished EL panel made accordingto the principles of the present invention, used to display an imageconsisting of the alphanumeric characters "A" and "E."

FIG. 4 is a cross-section of a sheet having substrate and conductorlayers; the sheet is preferably commercially purchased and forms thestarting point for building the preferred EL panel.

FIG. 5 shows the sheet of FIG. 4, having the conductive layer removed ina small corner of the panel to expose substrate.

FIG. 6 shows the panel of FIG. 5, taken along lines 6--6 of FIG. 5.

FIG. 7 shows the panel of FIG. 5 and a patterned insulator layer whichhas been deposited on top of the layers seen in FIG. 5 (to formalphanumeric characters "A" and "E" as seen in FIG. 8) to thereby form aprefabricated assembly.

FIG. 8 shows the prefabricated assembly of FIG. 7, taken along lines8--8 of FIG. 7.

FIG. 9 shows the prefabricated assembly of FIG. 8 as it is fitted with adeposition frame; the frame is added for vacuum deposition of ELmaterials, magnesium and silver layers, and it limits the region ofdeposition.

FIG. 10 schematically shows a vacuum deposition chamber with theprefabricated assembly and deposition frame clamped to it.

FIG. 11 shows the prefabricated assembly of FIG. 9 and layers of ELmaterials deposited on top of the prefabricated assembly, within theregion defined by the frame.

FIG. 12 indicates deposition of a first electrode material (magnesium)on top of the layers of EL materials of FIG. 11, within the regiondefined by the frame.

FIG. 13 indicates deposition of a metal cap (silver) on top of themagnesium layer of FIG. 12, within the region defined by the frame, toform a finished EL panel.

FIG. 14 shows the finished EL panel of FIG. 13, with the frame removed.

FIG. 15 shows the EL panel of FIG. 14 with positive and negativeterminals attached to first and second regions of the display.

FIG. 16 shows a camera, computer and printer used to create aphotoresist mask for patterning the insulator; in the preferred exampleshown, a simple transparency is generated to be used as a photoresistmask.

FIG. 17 is a schematic view that indicates (a) adherence of thephotoresist mask to the material of FIGS. 5 and 6 (which has beenlayered with a patternable insulator which is a photoresist) and (b)exposure of the photoresist to form an exposed material.

FIG. 18 shows chemical development of the exposed material, whereby thepatternable insulator has now been patterned in the form of alphanumericcharacters "A" and "E," to form the prefabricated assembly of FIG. 8.

DETAILED DESCRIPTION

The invention summarized above and defined by the enumerated claims maybe better understood by referring to the following detailed description,which should be read in conjunction with the accompanying drawings. Thisdetailed description of a particular preferred embodiment, set out belowto enable one to build and use one particular implementation of theinvention, is not intended to limit the enumerated claims, but to serveas a particular example thereof. The particular example set out below isthe preferred specific implementation of an electroluminescent ("EL")display device, namely, an organic EL display device having a patternedinsulator. The invention, however, may also be applied to other types ofsystems as well, including inorganic devices.

I. Introduction to the Principal Parts.

In accordance with the principles of the present invention, thepreferred embodiment is an organic EL display device and procedure forfabricating that device. In particular, the device is used to display animage using a single large pixel EL display element (or "panel") thatrepresents multiple visual attributes; alternatively, a composite imagecan be formed using multiple, tiled panels, each of which representsmultiple visual attributes. Each panel has an insulator layer whichpermits varied illumination, such that the panel represents a pluralityof commonly-controlled visual attributes.

With reference to FIG. 2, the preferred panel 101 includes a pluralityof thin-film layers (105, 107, 109 and 111) which are arranged upon asupporting substrate 103. These layers will first be briefly introducedprior to describing the preferred fabrication process.

The substrate 103 is purchased from a commercial source, preferably witha 500-to-3000 Angstrom-thick layer of indium tin oxide ("ITO") 105already sputtered onto the substrate. It is this layer 105 of ITO whichwill form a first electrode (the anode) used to provide a current pathfor illuminating the EL panel 101. As will be described below, thiscommercially-purchased combination is then processed to add: (1) apatterned insulator 107, which is preferably created using acommercially available photoresist ("AZ 1512," made by HoechstCelanese); (2) two organic EL material layers 109 and 110, (including ahole transport layer 109 and electron transport layer 110,respectively); (3) a second electrode 111 (preferably, magnesium), whichis vacuum-deposited on top of the organic EL material layers to form acathode; and (4) a cap layer 113 of silver, which is deposited in thesame vacuum as the magnesium (to cap the magnesium, which is typicallyair-sensitive).

The preferred patterned insulator layer 107 is implemented as aphotoresist that is exposed and developed to provide to any desiredimage. As a result, the insulator layer 107 will, when developed, have apattern of electrical insulation where current (a) in some areas 115 isrelatively unimpeded (and thus, the current is permitted to locally passthrough the EL material layers 109 and generate light), and (b) in otherareas 117 is relatively impeded, and thus, which inhibits localgeneration of light. In the particular example of FIG. 2, the areas 115and 117 are indicated to have either no insulation and full insulation,respectively, corresponding to maximum light generation from the ELlayers 109 and 110, and no luminescence; preferably, different grayscale levels may be produced by half-toning procedures; however, it isto be understood that varied levels of insulation can also be providedusing suitable patterning procedures, to cause luminescence betweenthese extremes.

FIG. 3 provides an illustrative display of the alphanumeric characters"A" and "E." In this example, regions within the boundaries of thecharacters "A" and "E" correspond to areas 115 having no insulation, andthese areas will luminesce when a voltage is coupled across terminalregions 119 and 121. By contrast, the remainder of the display featuresa relatively thick layer of insulation between the electrodes, and nolight is generated in those areas. The hypothetical display image ofcharacters "A" and "E" will be referenced in the remainder of figuresdiscussed by this disclosure.

The preferred method of exposing the photoresist (to display characters"A" and "E") uses a transparency having a computer image printed on it;since present day computer image processing abilities are sufficientlysophisticated to manipulate and print image of nearly any resolution,including photographic images, the preferred method is used to develop aphotoresist mask representing nearly any desired image, no matter howcomplex. The photoresist is preferably added atop the ITO layer 105(FIG. 2) in an initial processing step, prior to vacuum deposition ofthe remaining layers 109, 110, 111 and 113. Once the photoresist hasbeen exposed using the photoresist mask and subsequently developed, aprefabricated assembly is formed which is adapted to single-vacuumcompletion of the panel 101. In this manner, with image patterningalready achieved, completion of the EL device can occur withoutintricate etching and cleaning operations which might be required wereit necessary to interrupt a vacuum to pattern the cathode 111.

With reference to FIG. 15, another feature of the preferred EL panel 101is the fabrication of three regions 119, 121 and 123 of the device,including (1) a first terminal region 119 that will serve as anelectrical terminal for the cathode, (2) a second terminal region 121that will serve as an electrical terminal for the anode, and (3) a thirdregion 123 where the desired image display is to be formed.

The first region 119 is formed by first defining an area that issufficiently large to serve as an electrical terminal connection (forexample, by selecting an area for coupling to electrical conductingclips). From this region only, the ITO layer is removed to expose asmall corner 125 of the substrate. During addition of, and exposure ofthe photoresist, a border region 127 (FIG. 15) of insulation is formedthat overlies and insulates at least a small periphery of theITO/exposed substrate interface. During vacuum deposition upon theprefabricated assembly to add the organic EL, cathode and cap layers, adeposition frame (not seen in FIG. 15) is chosen such that these layersare deposited over the small corner 125 of the substrate. Uponcompletion, this first region 119 will include organic EL, magnesium andsilver all overlying the substrate, but not include any underlying ITO.Consequently, when an electrical terminal is connected to the region119, there is little danger of breaking through unintentionally shortingthe panel 101 by breaking through the organic EL and insulator layers.

The second region 121 conversely includes an exposed ITO layer 105, buthas no cathode or cap layer. This configuration also reduces thelikelihood of unintentionally shorting the panel during connection of asecond electrical terminal. In forming the second region 121, a secondsmall area 131 or corner is chosen that will also be suitable forconnection of a second electrical terminal such as via an electricalconducting clip. Care is taken to ensure that the photoresist layer isnot added to completely overlie this area, but rather, to leave the ITOlayer 105 exposed within the second small area 131. In addition, duringthe vacuum deposition, care is also taken to (1) choose a depositionframe and place it such that the organic EL, cathode and cap layers donot overlie the second small area 131, and (2) leave a suitable border133 of photoresist material that buffers the interface of the ITO layer105 and the organic EL, cathode and cap layers.

Finally, a third region 123 is also created for display of the desiredimage, e.g., the alphanumeric characters "A" and "E;" this third regionfeatures all of the organic EL materials, and both anode and cathode inoverlapping relationship (with the patterned insulator used todifferentiate different visual attributes). FIG. 15 shows the panel 101of FIG. 3 with clips 135 and 137 coupled to the first two regions 119and 121, to cause the third region 123 to luminesce. Notably, as seen inFIG. 15, there are no connecting bridges or other undesired paths whichare illuminated; rather, the image formed is exactly the image desired,e.g., the alphanumeric characters "A" and "E" alone.

II. Fabrication of the EL Panel's Layers.

The process of forming an EL panel will now be described in greaterdetail, with reference to FIGS. 4-15, which indicate the processing ofthe panel from purchase of a commercial substrate/ITO package 147 (FIG.4) to the preferred, finished panel 101 (FIG. 15). As mentioned earlier,the preferred fabrication process includes development of aprefabricated assembly 139 (FIGS. 7-8), and subsequently, a singlevacuum deposition process which utilizes a suitable deposition frame 141selected and placed to facilitate development of first and secondterminal regions 119 and 121 (FIG. 15).

The preferred fabrication procedure utilizes a commercially purchasedsubstrate/ITO package 147, indicated in FIG. 4. As mentioned earlier,the ITO layer 105 has preferably already been added to the substrate 103(which is formed of glass, approximately one millimeter thick) at thetime of purchase via a standard sputtering process. Preliminarily, thepackage 147 is cut or shaped from a sheet of material to beapproximately two-by-three inches in width and length (as suitable foruse in standard wafer deposition equipment). Subsequently, the package147 is processed to develop the prefabricated assembly 139 (FIGS. 7 and8) by first chemically etching the ITO layer 105 to expose the smallcorner 125 of the substrate, and then, by adding, exposing anddeveloping a photoresist layer 151.

Prior to adding the photoresist layer 151, the package 147 (FIGS. 5 and6) is cleaned to ensure a smooth adherence of the photoresist layer tothe ITO layer 105. First, the package 147 is immersed in an ultrasonicbath which includes a mixture of "Acacianox" and deionized, distilledwater. Following the ultrasonic bath, the package 147 is rinsed insuccessive five minute baths of deionized, distilled water, acetone andisopropyl alcohol. The package 147 is dried using dry nitrogen and abaking procedure of one-hundred-and-thirty degrees Celsius forapproximately ten minutes.

Following the cleaning procedure, the photoresist material 151 is addedto create a uniform 0.5-to-10 micron layer by spin coating the ITO layer105 to overlie all portions of the package 147. Preferably, the spincoating procedure utilizes a spin rate of about 3000-to 6000-rotationsper minute and a duration of less than one minute, depending upon thedesired deposition rate.

Importantly, the photoresist layer 151 is employed as an insulatormaterial because it is easily exposed to a predetermined image and thendeveloped into a patterned electrical insulator. Exposure anddevelopment of a photoresist layer 151 is the preferred method ofpatterning, but there are other materials which may be used to develop apatterned insulator; for example, acceptable methods would include useof a pre-patterned adhesive insulator or a chemically-etched insulator.Other types of insulators or patterning methods will occur to those ofordinary skill in the art. Deposition of a photoresist layer 151 isespecially useful, however, because a laser printer (not seen in FIGS.4-15) can be conveniently used to create a photomask via printing upon atransparency, thereby relying on the image processing abilities of manyof today's image processing computers (including the ability to acceptphotographs and generate complex computer images). This photomaskproduction step using a laser printer does not give perfect results, butis a low-cost, practical approach to developing an intricate displayimage. When the photoresist is developed, the resultant patternedinsulator layer 107 may also be tailored to have gradual corners 150 asseen in FIG. 7, rather than sharp corners; this advantage facilitatesbetter device reliability with a reduced likelihood of unintendedelectrical shortage between electrodes. The preferred method ofpatterning the photoresist, following the spin-coat process, isdescribed further below.

Whichever patterning procedure is utilized, the insulator layer (107,151) is patterned so as to retard the flow of current through it inproportion to the areas of the desired display that are to be relativelydark. For example, with reference to FIG. 8, since it is desired toilluminate the letters "A" and "E" only, the photoresist layer 107 ispatterned to expose the ITO layer in these locations 152 within thecharacters' boundaries, so that relatively little electrical resistanceis provided between the cathode and anode layers (through the ELmaterials) at these locations.

FIGS. 7 and 8 show the prefabricated assembly 139, where all processingprior to a single step vacuum has been performed, and the remaininglayers of the EL device can be added without patterning or interruptingthe vacuum. As can be seen in these figures, the photoresist layer 151has been added atop the ITO layer 105 and the substrate 103 to cover allareas except the portions of the display for which it is desired to emitlight, namely, as defined by the alphanumeric characters "A" and "E."Within these characters, the ITO layer 105 remains exposed; for purposesof illustration, FIG. 8 shows the small corner 125 to be used for anelectrical terminal as exposed, although in practice it may be coveredwith photoresist material since the cathode will be deposited over thecorner 125 in the vacuum deposition process, and it is important only toremove underlying ITO from within the corner 125 to reduce thelikelihood of electrical short.

FIGS. 9-14 illustrate deposition of additional layers in a single-vacuumprocedure. In FIG. 9, the prefabricated assembly 139 is shown with thedeposition frame 141 clamped onto it, thereby defining a deposition area159 within the frame's boundaries. Although the frame 141 is illustratedby a black rectangle in FIG. 9, with the remainder of the prefabricatedassembly 139 outside of the rectangle visible, it is to be understoodthat the frame completely masks all portions of the panel not indicatedwithin the frame's boundaries. Importantly, the frame 141 is chosen topermit deposition in the first terminal region indicated in thelower-right hand of FIG. 9 by the reference numeral 143 (this areaoverlaps the small corner 125 to the maximum extent possible).

The prefabricated assembly 139, with the frame 141 clamped onto it, isseen in FIG. 10 to be mounted within a vacuum chamber 163 for vapordeposition, thermal evaporation or other deposition process conventionalto thin-film fabrication. As seen in FIG. 10, the preferred methodutilizes a thermal evaporation (vapor deposition) source 165 mountedwithin the chamber 163; four particular sources 167-170 are illustrated,corresponding to each of hole transport EL material, electron transportEL material, cathode material and cap material. Each source 165 includesa crucible 171 and a heated filament 172 which is selectively engagedwhen source shutters 173 are opened to permit vapor deposition ofmaterial within the crucible. As seen in FIG. 10, the prefabricatedassembly 139 is continually rotated during deposition to promote uniformlayer thickness, as indicated by the arrow 175. A second arrow 177indicates that individual shutters associated with each source 167-170are sequentially opened for selective deposition of the appropriatematerial. Finally, a third arrow 178 is also used to show depositiononto the prefabricated assembly. All of the layers are sequentiallydeposited without interrupting the vacuum, such that the air sensitivelayers (typically, the organic EL and cathode layers) can be sealed.

As indicated in FIG. 11, the area 159 within the boundaries of the frame141 is first deposited with two organic EL layers (collectively, 179),namely, the hole transport layer 109 and the electron transport layer110 (indicated earlier in FIG. 2). Each of these layers is typicallysix-to-eight hundred Angstroms in thickness. The hole transport layer109 is preferably formed first, by vapor deposition ofN,N'-diphenyl-N-N'-bis(3-methylphenyl)1,1'-biphenyl-4,4"diamine ("TPD").Next, the electron transport layer 110 is formed of aluminumtrihydroxyquinoline (Alq₃), also by vapor deposition. Many differentcompounds and variations in structure have been used for the differentlayers and regions in organic electroluminescent devices. Examples ofsuch devices and the specific compounds of which they are made are foundin such references as U.S. Pat. No. 4,356,429 (Tang) issued Oct. 26,1982; U.S. Pat. No. 4,539,507 (VanSlyke et al.) issued Sep. 3, 1985;U.S. Pat. No. 4,885,211 (Tang et al.) issued Dec. 5, 1989; U.S. Pat. No.5,047,687 (VanSlyke) issued Sep. 10, 1991; U.S. Pat. No. 5,059,862(VanSlyke et al.) issued Oct. 22, 1991; and Tang et al.,"Electroluminescence of Doped Organic Thin Films", Journal of AppliedPhysics no. 65(9), May 1, 1989, pages 3610-3616, all of which areincorporated herein by this reference.

Once the organic EL layers 179 are deposited, cathode and cap layers 181and 183 (FIGS. 12 and 13) are deposited using an evaporation process tocomplete fabrication of an organic EL panel 101 (FIG. 15). As indicatedby angled-line hatching in FIG. 12, the magnesium (cathode) layer 181 isdeposited on top of the electron transport layer without interruptingthe vacuum, preferably having a thickness of about fifteen-hundredAngstroms. Immediately following this deposition, the layer 183 ofsilver (or alternatively, aluminum) is deposited to have a thickness ofbetween two-tenths-to-two microns, as indicated by FIG. 13. This final"cap" layer 183 serves to insulate the magnesium layer 181 from air, andto reduce the likelihood that any holes exist in the cathode layer whichcould be a source for air or water, which might detract from thedevice's useful life. FIG. 13 indicates addition of the silver layer 183using a different hatching than was used in connection with FIG. 12,whereas FIG. 14 indicates configuration of the completed EL panel 101after removal from the vacuum chamber 163 and removal of the depositionframe 141 from the completed panel. In FIG. 14, a left edge 187 of thepanel exposes the ITO layer 105, whereas a right lower corner 189 of thepanel features exposed silver without ITO lying beneath the silver.

III. Configuration of Electrical Terminals.

Electrical terminals can then be attached as indicated in FIG. 15 tocause the desired display of the alphanumeric characters "A" and "E" tobe illuminated at regions which are relatively unimpeded by thepatterned insulator layer. The terminals can be as simple as electricalconducting clips 135 and 137, or may be made to be more permanent innature. Typically, a supply voltage (not seen) of between 2.50-and-15volts is used to cause illumination of the panel 101, depending upon thethickness of the organic EL layers.

IV. Patterning the Insulator.

A. Use of A Photoresist.

In accordance with the principles of the invention, various mechanismscan be used to generate the patterned insulator layer. Preferably, asindicated by FIG. 16, a desired image is generated by a computer 191, oris captured by a video camera 193 which is connected to the computer forimage processing and printout. Use of a computer 191 enables creation ofmasks that utilize highly detailed images, such as digital photographsor other complex images.

A laser printer 195 is then used to print the desired display upon atransparency 197 that will be used to expose the "AZ 1512" positivephotoresist material. The laser printer 195 is caused to print onlythose portions of the transparency 197 which will be illuminated using apositive photoresist. For example, as seen in FIG. 16, a computer image199 of the alphanumeric characters "A" and "E" is printed upon thetransparency 197 such that the letters are black.

Notably, it will readily occur to one of ordinary skill in the art thatmany different types of masks can be used instead of a transparency. Forexample, standard photomasks used in integrated circuits, or thermalmask procedures can be used.

In the case of the preferred photoresist material ("AZ 1512"), exposureand development occurs by first applying a soft bake procedure to thedeposited photoresist material (designated by the reference numeral 201in FIG. 17) of about ninety degrees Celsius for five minutes, and thenallowing the material to cool to room temperature. The transparency 197is then adhered or taped to overlie the photoresist material 201, whichis then exposed to an ultraviolet lamp 205 for approximately one minutein a manner that provides for uniform illumination. Following exposure,the transparency 197 is removed and development is performed asindicated by FIG. 18 by immersing the exposed package 203 in a 50/50bath 206 of developer ("AZ 1512" developer, made by Hoeschst Celanese)and deionized, distilled water for approximately one hour. The package203 is then washed in running water to removed any undesired photoresistfilm residuals, to produce the prefabricated assembly 139. Theprefabricated assembly 139 is then dried using dry nitrogen andsubjected to a bake procedure of one-hundred-and-thirty degrees Celsiusfor five-to-ten minutes. The prefabricated assembly 139 is then readyfor vacuum deposition of the organic EL layer 179 using thermalprocedures.

B. Use of Other Patterning Methods.

While use of a photoresist material is the preferred method ofpatterning the preferred insulator layer 107 of the panel 101 (asindicated by FIG. 3), there are other methods which can be employed aswell. For example, a precision-controlled laser (not seen) can beutilized to pattern the insulator layer. Alternatively, a chemical etchprocess can be utilized where a chemical etch material is deposited asthe insulator layer and a suitable mask is patterned on top of theinsulator layer. This method is schematically also depicted by FIG. 17,with the letters "A" and "E" 207 representing a chemical mask which hasbeen adhered to an etch material to resist chemical erosion. Asindicated by FIG. 18, the composite may then also be developed using anappropriate bath 206, and the mask 207 removed to leave a patternedinsulator. Alternatively, other insulators may be used other than aphotoresist, for example, a silicon oxide or silicon nitride layer,coupled with suitable patterning procedures. These methods are not theonly patterning mechanisms which will occur to those having ordinaryskill in the art, and a variety of other patterning procedures may beused to create the patterned insulator layer. In addition, it is withinthe scope of the present invention to utilize both electrode patterningand use of a patterned insulator.

Having thus described an exemplary embodiment of the invention, it willbe apparent that further alterations, modifications, and improvementswill also occur to those skilled in the art. Further, it will beapparent that the present invention is not limited to the specific formdescribed. Rather, the preferred display, and the invention in general,may be applied to a wide variety of applications. Various alterations,modifications, and improvements, though not expressly described ormentioned above, are nonetheless intended and implied to be within thespirit and scope of the invention. Accordingly, the foregoing discussionis intended to be illustrative only; the invention is limited anddefined only by the various following claims and equivalents thereto.

We claim:
 1. An electroluminescent display device having two conductorsand an electroluminescent material therebetween, the electroluminescentmaterial adapted to luminesce when electricity flows through it, theimprovement comprising:the first and second conductors and theelectroluminescent material layered to form a substantially flat displaypanel with the electroluminescent material between the conductors, thesubstantially flat display panel including three regions, including adisplay region and first and second terminal regions; and a patternedinsulator, layered between the first and second conductors, thepatterned insulator possessing substantial breaks and continuitieswithin the display region to thereby form a pattern that selectivelyinhibits electrical flow at predetermined areas of the display region,thereby causing the electroluminescent material to luminesce only atportions of the display region not electrically inhibited by thepatterned insulator; and wherein the first electrode is layered suchthat the first electrode occupies only the display region and the firstterminal region, and wherein the second electrode and theelectroluminescent material are layered to occupy only the displayregion and the second terminal region, such that two mutually-exclusiveregions are thereby formed outside the display region, each containingone of the first and second electrodes, but not both, such that risk ofelectrical shortage between layers of the display device is therebyreduced during electrical connection to each of the twomutually-exclusive regions.
 2. An improvement according to claim 1,further comprising:a display region that includes organicelectroluminescent material.
 3. An improvement according to claim 1,further comprising:a display region that includes an air-sensitiveelectrode layer and a cap layer that is deposited atop the displayregion, to seal the display region from external exposure.
 4. Animprovement according to claim 1, wherein the electroluminescentmaterial is an organic electroluminescent material.
 5. Anelectroluminescent display device, comprising:a substrate having first,second and third regions; an anode layer layered above the substrate tocover the second region and the third region only; a cathode layerlayered above the substrate to cover the first region and the thirdregion only; an electroluminescent material layered between the anodelayer and the cathode layer that covers the third region and one of thefirst and second regions; and a patterned insulator layered between theanode layer and cathode layer, the patterned insulator possessingsubstantial breaks and continuities within the display region to therebyform a pattern that selectively inhibits electrical flow atpredetermined areas of the display region, thereby causing theelectroluminescent material to luminesce only at portions of the displayregion not electrically inhibited by the patterned insulator.
 6. Adevice according to claim 5, wherein the electroluminescent material andone of the anode layer and the cathode layer are formed by deposition ina common vacuum using a common mask.
 7. A device according to claim 5,wherein the electroluminescent material is an organic electroluminescentmaterial.
 8. A device according to claim 5, wherein the first regionincludes an exposed cathode layer, and wherein the second regionincludes an exposed anode layer, underlying electroluminescent material,and no underlying anode layer.
 9. A method of making anelectroluminescent display, comprising:depositing each of a cathodelayer and an anode layer; depositing an electroluminescent materialbetween the cathode layer and the anode layer, the electroluminescentmaterial emitting radiation when current flows through theelectroluminescent material between the cathode layer and the anodelayer; and forming a patterned insulator layer to thereby create variedelectrical insulation between the cathode layer and the anode layer atdifferent regions of said display by depositing a photosensitivematerial and patterning it byexposing the photosensitive material usingan illumination device and an image, and developing the photosensitivematerial to form a patterned insulator layer, by removing exposedregions of photosensitive material if the photosensitive material is apositive photoresist, and by removing unexposed regions ofphotosensitive material if the photosensitive material is a negativephotoresist; whereinconductive regions of said display are therebyformed which have relatively high electrical conductivity, and therebyemit relatively greater radiation when current flows between the cathodelayer and the anode layer, and impeded regions of said display arethereby also formed, which have relatively low electrical conductivity,and thereby emit relatively less radiation when current flows betweenthe cathode layer and the anode layer.
 10. A method of making anelectroluminescent display according to claim 9, furthercomprising:creating a prefabricated assembly that includes a substrate,one of the cathode layer and the anode layer over the substrate, and apatterned insulator layer over the one of the cathode layer and theanode layer; and depositing in a single vacuum the electroluminescentmaterial over the patterned insulator layer, and the other of thecathode layer and the anode layer over the electroluminescent material.11. A method of making an electroluminescent display according to claim10, wherein depositing in a single vacuum includes:depositing the otherof the cathode layer and the anode layer to include both of a firstconductor layer that is sensitive to exposure to air; and depositing asecond conductor layer over the first conductive layer, the secondconductive layer being relatively insensitive to air and substantiallysealing the first conductive layer from exposure to air.
 12. A method ofmaking an electroluminescent display according to claim 10, whereindepositing in a single vacuum includes:depositing the electroluminescentmaterial to include both of a hole transport layer and an electrontransport layer.
 13. A method of making an electroluminescent displayaccording to claim 9, wherein:depositing the electroluminescent materialincludes depositing an organic electroluminescent material.
 14. A methodof making an electroluminescent display according to claim 9, whereinexposing the photosensitive material includes:placing a mask layer overthe photosensitive material, the mask layer patterned to selectivelyadmit and block light at different regions of said display; andilluminating the mask layer with the light to thereby expose selectiveregions of the photosensitive material.
 15. A method of making anelectroluminescent display according to claim 14, wherein:said methodfurther comprises generating the mask layer by using a computer and alaser printer to print an image upon a transparency; and placing themask layer over the photosensitive material includes placing thetransparency and the image printed upon it over the photosensitivematerial.
 16. A method of making an electroluminescent display,comprising:creating a prefabricated assembly that includes a substrate,one of a cathode layer and the anode layer over the substrate, and apatterned insulator layer over the one of the cathode layer and theanode layer; and depositing in a single vacuum an electroluminescentmaterial layer over the patterned insulator layer, and the other of thecathode layer and the anode layer over the electroluminescentmaterial;wherein conductive regions of said display are formed (viapatterning in the patterned insulator layer) which have relatively highelectrical conductivity, and thereby emit relatively greater radiationwhen current flows between the cathode layer and the anode layer, andimpeded regions of said display are also formed (via insulation providedby the patterned insulator layer) which have relatively low electricalconductivity, and thereby emit relatively less radiation when currentflows between the cathode layer and the anode layer.
 17. A method ofmaking an electroluminescent display according to claim 16, whereindepositing in a single vacuum includes:depositing the other of thecathode layer and the anode layer to include both of a first conductorlayer that is sensitive to exposure to air; and depositing a secondconductor layer over the first conductive layer, the second conductivelayer being relatively insensitive to air and substantially sealing thefirst conductive layer from exposure to air.
 18. A method of making anelectroluminescent display according to claim 16, wherein depositing ina single vacuum includes:depositing the electroluminescent material toinclude both of a hole transport layer and an electron transport layer.19. A method of making an electroluminescent display according to claim16, wherein:depositing the electroluminescent material includesdepositing an organic electroluminescent material.
 20. A method ofmaking an electroluminescent display according to claim 16, whereindepositing an insulator layer includes:depositing a photosensitivematerial; and forming a pattern byplacing a mask layer over thephotosensitive material, the mask layer patterned to selectively admitand block light at different regions of said display; and exposing thephotosensitive material to the light, with the mask layer in place, tothereby expose selective regions of the photosensitive material, anddeveloping the photosensitive material to form the patterned insulatorlayer, by removing exposed regions of photosensitive material if thephotosensitive material is a positive photoresist and by removingunexposed regions of photosensitive material if the photosensitivematerial is a negative photoresist.
 21. A method of making anelectroluminescent display according to claim 20, wherein:said methodfurther comprises generating the mask layer by using a computer and alaser printer to print an image upon a transparency; and placing themask layer over the photosensitive material includes placing thetransparency and the image printed upon it over the photosensitivematerial.
 22. A method of making an electroluminescent display accordingto claim 16, wherein forming a pattern includes:adhering a mask layerover the insulator layer, the mask layer selected to resist apredetermined etch chemical, and with the mask layer in place,chemically etching the portions of the insulator layer exposed by themask layer.
 23. A method of making an electroluminescent displayaccording to claim 9, wherein the electroluminescent display includes asubstrate having at least three regions, and wherein:depositing each ofthe anode layer and the cathode layer includesdepositing one of theanode layer and the cathode layer over the substrate to cover all but afirst one of the three regions, and depositing the other of the anodelayer and the cathode layer over the substrate to cover all but a secondone of the regions; and depositing the electroluminescent materialincludes depositing the electroluminescent material such that it coversthe third region, which is overlaid by all three of the anode layer, thecathode layer and the electroluminescent material; wherein, aftercompletion of the electroluminescent display,the first one of theregions is thereby adapted for use as a first electrical terminal whichis not susceptible to electrical shorting via layer damage, the secondone of the regions is thereby adapted for use as a second electricalterminal which is not susceptible to electrical shorting via layerdamage, and the third one of the regions is thereby adapted for use ingenerating radiation when electrical current flows between the first andsecond electrical terminals.
 24. A method of making anelectroluminescent display according to claim 23, furthercomprising:creating a prefabricated assembly to includeone of thecathode layer and the anode layer over the substrate in a manner tocover the first and third ones of the regions, and a patterned insulatorlayer over the substrate in a manner that covers at least the third oneof the regions; and depositing in a single vacuum with a single mask theelectroluminescent material, and the other of the cathode layer and theanode layer, the mask oriented such that the electroluminescent materialand the other of the cathode layer and the anode layer cover at leastthe second and third ones of the regions.